Study on Flow Fields of Boundary-Layer Separation and Hydraulic Jump during Rundown Motion of Shoaling Solitary Wave

Chang Lin, Ming Jer Kao, Guang Wei Tzeng, Wei Ying Wong, James Yang, Rajkumar V. Raikar, Tso Ren Wu, Philip Li Fang Liu

Research output: Contribution to journalArticlepeer-review

17 Scopus citations

Abstract

The characteristics of flow fields for a complete evolution of the non-breaking solitary wave, having a wave-height to water-depth ratio of 0.363 and propagating over a 1:5 sloping bottom, are investigated experimentally. This study mainly focuses on the occurrences of both flow separation on the boundary layer under an adverse pressure gradient and subsequent hydraulic jump with the abrupt rising of free surface during rundown motion of the shoaling wave, together with emphasis on the evolution of vortex structures underlying the separated shear layer and hydraulic jump. A flow visualization technique with particle trajectory method and a high-speed particle image velocimetry (HSPIV) system with a high-speed digital camera were used. Based on the instantaneous flow images visualized and/or the ensemble-averaged velocity fields measured, the following interesting features, which are unknown up-to-date, are presented and discussed in this study: (1) Flow bifurcation occurring on both offshore and onshore sides of the explicit demarcation curve and the stagnation point during runup motion; (2) The dependence of the diffuser-like flow field, being changed from the supercritical flow in the shallower region to the subcritical flow in the deeper counterpart, on the Froude number during the early and middle stages of rundown motion; (3) The positions and times for the occurrences of the incipient flow separation and the sudden rising of free surface of the hydraulic jump; (4) The associated movement and evolution of vortex structures under the separated shear layer, the hydraulic jump and/or the high-speed external main stream of the retreated flow; and (5) The entrainment of air bubbles from the free surface into the external main stream of the retreated flow.

Original languageEnglish
Article number1540002
JournalJournal of Earthquake and Tsunami
Volume9
Issue number5
DOIs
StatePublished - 1 Dec 2015

Keywords

  • flow separation
  • hydraulic jump
  • rundown
  • runup
  • separated shear layer
  • Shoaling solitary wave
  • vortex structure

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